The following Patent Literatures describe a suspension system for a vehicle having shock absorbers each of which includes a damping-force changing mechanism for changing a magnitude of a damping force with respect to a relative movement of a sprung portion and an unsprung portion and each of which is configured to generate the damping force with respect to the relative movement of the sprung portion and the unsprung portion such that the magnitude of the damping force is changeable. As described in the following Patent Literatures, there are various techniques of controlling the damping force by controlling the damping-force changing mechanism.
Patent Literature 1: JP-A-3-42320
Patent Literature 2: WO/2012/032655
Patent Literature 3: JP-A-5-124413